More precisely, the invention relates to a process, and to the installation allowing its implementation, which consists in applying, to a web of yarns continuously deposited on a moving substrate, a powder of a material capable of reacting under the effect of heat in order to form a coating layer, said web comprising at least one organic, thermoplastic or thermosetting, material and at least one reinforcing material, and in heating and then compressing the assembly thus obtained in order to form a composite sheet.
The walls of trucks, trailers and containers used for transporting or storing merchandise are formed from panels generally consisting of a thermoplastic or thermosetting material into which reinforcing yarns, especially glass yarns, are incorporated, and of a topcoat whose function is to improve the appearance of the surface visible from the outside. The main purpose of the topcoat is to attenuate the “marking” effect due to the presence of the reinforcing yarns near the surface, in other words to make it smoother and possibly glossier. The esthetic appearance is not the only advantage provided by the coat: since the surface finish is improved, it becomes easier to apply patterns and inscriptions, for example by means of a paint or in the form of stickers, or to maintain the state of cleanliness thereof.
The walls of trucks, trailers and containers each consist of a one-piece panel of large dimensions, possibly up to 3.5 meters in width and 17 meters in length, or even more.
Several known methods are used to manufacture these panels.
A first method consists in forming a continuous strip from a matrix comprising reinforcing yarns, in coating this strip with a film capable of forming the coating layer and in cutting said strip to the required dimensions in order to form the final composite panel.
To obtain very wide panels requires the use of a film at least as wide as that of the panel. It is difficult and also very expensive to produce such films, as the production requires machines that are specially adapted to these large widths. The film may be obtained and deposited directly by extrusion at the time of manufacture of the panel or the film may be provided already wound in the form of reels. For widths greater than 2 meters, it is not conceivable to use extrusion since the cost of the machine is much too high.
With reels, there are additional problems associated with production (size of the reels, quality of the film), with storage and with the requirement to have a specific film for each type of panel, especially as regards the color. Conventionally, these drawbacks are alleviated by using several films of smaller width that are juxtaposed or partially overlapped at the edges in order to be matched to the size of the panel. However, the final panel is unsatisfactory as marks remain visible where the films are joined together.
Another method consists in cutting the strip from the abovementioned first method to the dimensions of the panel and then in applying the coating in paint form.
The nature of the material used does not allow correct bonding of the paint when it is applied directly. It is for this reason that it is generally recommended to pretreat the surface to be coated, for example by applying an adhesion primer or else to carry out a flame treatment (“flame brushing”) or a corona treatment. It is general practice to apply a layer of a “lining” primer to the treated surface, said primer having the consistency of a mastic and serving to mask the surface irregularities. The coat of paint that forms the actual topcoat is applied to the primer, possibly after a rubbing-down step.
Although this method allows great freedom in the choice of color, it also has drawbacks. Its implementation requires a painting booth capable of taking large panels, and also having to be equipped with means for the completely safe use of paints based on organic solvents that are undesirable both for users and for the environment, and for keeping the panels free of dust.
The above process is a discontinuous process in which each panel is treated individually in a relatively long treatment cycle: to give an example, with the adhesion primer, several hours of drying are needed before the next layers can be applied.
It is an object of the present invention to provide a process that allows rapid and continuous manufacture of composite sheets which have a coating improving the surface appearance and are of large dimensions, especially a large width.
It is also an object of the present invention to provide a process in which the coating is formed on the composite sheet by applying a powder.